1. Field of the Invention
The present invention relates to a filler material to be used at the time of welding aluminum alloy die-cast members by laser welding for example. It also relates to a welding method using such filler material and a welded article.
2. Description of Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
For example, one of the most effective ways to attain high mileage of automobiles is to reduce the weight of the automobile. Accordingly, active attempts to replace conventional iron parts of automobiles with aluminum alloy parts have been performed.
However, merely replacing conventional iron material with aluminum alloy causes a substantially increased manufacturing cost.
Under the circumstances, in order to attain low-cost aluminum alloy automobile members, e.g., body members, chassis members and suspension members, it has just begun to use aluminum alloy die-cast members as space frame joints or B-pillars for example.
As a method of joining an aluminum alloy die-cast member to an aluminum alloy die-cast member or a die-cast member to a non-die-cast member, mechanical joining using rivets or welding using high density energy heat resource such as laser welding, electron beam welding or arc welding (MIG welding) has been employed.
When the aforementioned welding members such as aluminum alloy die-cast members are welded, there are problems that a large amount of blowholes will be generated in the welded portion to cause a deterioration of the strength. This mainly results from the fact that a large amount of gases such as air are involved in the die-cast member due to the inherent features of die-casting method and that these gases will be emitted at the time of welding.
Although the generation of the aforementioned blowholes can be prevented by strictly controlling the gas content in the die-cast member, this requires to improve the quality of die-cast member, resulting in an increased cost.
This problem occurs not only at the time of welding two welding members including at least one aluminum alloy die-cast member but also at the time of performing bead-on welding for the purpose of improving the surface quality of welding members.
Under the circumstances, for the purpose of suppressing the generation of blowholes at the time of welding aluminum alloy die-cast welding members, the present inventors proposed an aluminum alloy filler wire for use in laser welding as disclosed in Japanese Unexamined Laid-open Patent Publication No. 2002-239782. In this proposed filler wire, the content of Al—K—F series flux to be contained in a filler is adjusted so as to satisfy the conditions of 1.5X−1.5≦Y≦2.0X and Y>0, wherein the hydrogen gas content in the aluminum alloy is represented by X cc/100 gAl and the mass ratio of the content of Al—K—F series flux contained in the filler is represented by Y %.
Furthermore, the present inventors proposed another aluminum alloy filler wire for use in laser welding as disclosed in Japanese Unexamined Laid-open Patent Publication No. 2001-353591. In this proposed filler wire, the mass ratio of the content of Al—K—F series flux contained in the filler is 0.05% or more but less than 1%.
As a conventional filler material capable of suppressing the generation of blowholes at the time of welding to improve the surface quality of aluminum alloy, Japanese Unexamined Laid-open Patent Publication No. 6-304780 proposes a welding aluminum wire in which a flux comprising Sodium (Na): 5 to 10%, Potassium (K): 40 to 45%, Oxygen(O): 5% or less, Sulfur (S): 5% or less, Fluorine (F): 5 to 10%, Chlorine (Cl): 35 to 40% is contained in the range of 0.1 to 8 wt %. Furthermore, Japanese Unexamined Laid-open Patent Publication No. 7-96396 proposes a welding aluminum filler material in which C2Cl6 powder is mixed by 0.05 to 20 wt %.
In recent years, for the purpose of attaining a further cost reduction at the time of applying aluminum alloy die-cast members to automobile members, non-heat treatment type aluminum alloy die-cast members, which does not require heat treatment after the die casting to adjust the mechanical property, have been developing.
This non-heat treatment type aluminum alloy die-cast material is, for example, an Al—Mg series alloy, an Al—Mg—Si series alloy, or an Al—Mg—Si—Mn series alloy, which contains Mg.
However, even in cases where non-heat treatment type aluminum die-cast members are welded by using filler material having the aforementioned blowhole generation suppressing effect, prescribed blowhole generation suppressing effect could not be attained. This is because Mg contained in the non-heat treatment type aluminum alloy die-cast members evaporates when melted at the time of welding and remains in the welded portion without being released therefrom.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.